Because of their special characteristics, components made of ceramic materials cannot, unlike for example metal components, be simply screwed to other components or be connected in a similar manner to other components. Ceramic components are very susceptible to breakage in particular in the event of point loads. For example the screwed connections exert substantial forces on the small contact areas of the pressing surface of the screw on the ceramic component. This loading can already lead to high local stresses at these contact regions and consequently to the failure of the ceramic due to fracture. Furthermore there is a notch effect at sharp edges of ceramic components such as are necessarily produced for example in the case of countersunk screws. These edges may therefore be starting points of cracks, which can in any case lead to the failure of the component in the medium term.
In particular if the ceramic components which are to be connected to other components are parts of prostheses and in particular parts of endoprostheses, such a failure of the ceramic component cannot be tolerated.
This problem is known per se. In the construction of prostheses, metal parts, in particular made of titanium and titanium alloys, are frequently used which can be screwed together without problems in order to ensure a secure connection between different components.
Ceramic components are often clamped to other components. An example of such clamping is conical clamping which is known for example from DE 43 35 931 B4. Here a ceramic component with a conical outer wall can be clamped in a metal component having a conical opening, wherein the cone of the ceramic component can have an angle different from the cone of the metal component.
The conical clamping makes possible a relatively large contact region by which point loads can be avoided. However, it has the disadvantage that the connection of the components cannot be secured against subsequent loosening. This may be problematic in particular when the ceramic component is part of a modular endoprosthesis which can only be assembled at the time of implantation into the body of the patient and of which the connection strength is dependent upon the surgeon. Such modular prostheses are used for example as hip joint or shoulder joint prostheses or also other small joint prostheses. The modular construction then comprises a stem which is for example metal and is driven into the thigh bone or the humerus. A ceramic ball is placed onto this stem as a replacement for the head of the thigh or humerus. The connection of the two components takes place by striking or impact of the head fitted onto the stem. In order to achieve a secure, non-positively engaged connection, however, the impact must take place with a precisely measured force and with a precise fit. If the fit is not optimal or the impact force is too low, the ceramic head can loosen. A secured firm connection, for example a screw connection, between the two prosthetic parts would therefore be desirable.